SVP 2021 abstracts – 06: Multituberculate bone histology more similar to placentals

You heard it here first (in 2016) when the large reptile tree (LRT, 1989+ taxa) nested multituberculates (Fig. 2) as derived members of the gnawing placental clade, Glires (subset Fig. 1). Multis experienced a reversal in the ear = posterior jaw bones due to the loosening and great movement of the dentary during the chewing cycle. That reversal made them appear to be pre-therians in the ear area only. The LRT uses traits from all parts of the body.

Weaver 2021 reports:
“The remarkable evolutionary success of placental mammals has been partly attributed to their reproductive strategy of prolonged gestation and birthing of precocial neonates. Although this strategy has conventionally been considered derived relative to that of marsupials with short gestation times and altricial neonates, mounting evidence has challenged this view, suggesting that the placental strategy may be plesiomorphic for therians (metatherian-marsupial and eutherian-placental lineages).”

Until this moment, I have never heard of any evidence
for any challenge to the traditional view. The LRT documents the arrival of placentals from marsupials, like Monodelphis, without a pouch. Basal placentals continue to give birth to tiny, helpless young.

Well (picture Dana Carvery as ‘the church lady‘), isn’t that interesting!

“That a clade of stem therians exhibits evidence of placental-like life histories lends support to the hypothesis that intense maternal-fetal contact characteristic of placentals is ancestral for Theria.”

This is incorrect. Stop trusting your out-of-date textbooks.
Add taxa to see where multis nest when given the opportunity to nest where they want to.

“Alternatively, multituberculates and placentals may have independently evolved similar life history strategies; convergent evolution of complex traits has been well documented in early mammalian evolution.”

No. Stop! Add taxa! Do the work!

“In either case, my results refute the hypothesis that the Cenozoic rise of placentals was driven by unique life history innovations and shed new light on the diversification and ecological
roles of mammals during the Mesozoic and early Cenozoic.”

Placentals first appeared in the Jurassic according to the LRT (Fig. 1).

References
Weaver LN 2021. Bone histology of multituberculate mammals points to a life history strategy similar to that of placentals, not marsupials. Journal of Vertebrate Paleontology abstracts.

wiki/Shenshou
wiki/Vilevolodon
wiki/Jeholbaatar
wiki/Rugosodon
wiki/Xianshou
wiki/Kryptobaatar
wiki/Ptilodus
wiki/Catopsbaatar
wki/Filikomys
wiki/Barbatodon